"El Quijote apócrifo" by Alonso Fernández de Avellaneda is a novel published in 1614 as an unauthorized sequel to Cervantes's "Don Quijote." When this rival version appeared, Cervantes was still writing his own continuation, spurring him to complete his official second part in 1615. The apocryphal work follows Don Quijote and Sancho Panza to Zaragoza for jousting tournaments, where they encounter noblemen who subject them to elaborate pranks and fictional adventures. The true identity of "Avellaneda" remains one of Spanish literature's greatest mysteries.
Wikipedia page about this book: es.wikipedia.org/wiki/Quijote_de_Avellaneda